rt2x00: Fix MAC address defines in rt61pci

The MAC address offset defines were incorrect because
the byte offset was used instead of word index. This
bug had no affect on normal operations since these
defines weren't used. (EEPROM_MAC_ADDR_0 was used
to read 6 bytes from).

Signed-off-by: Ivo van Doorn <IvDoorn@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>